H E AT / G A S L AW S
UE2040100
Boyle’s Law
UE2040100
B A SIC P RINCIP L E S
The volume of a fixed quantity of a gas depends on the pressure acting
on the gas and on the temperature of the gas. If the temperature
remains unchanged, the product of the volume and the temperature
remains constant in many cases. This law, discovered by Robert Boyle
and Edme Mariotte, is valid for all gases in the ideal state, which is
when the temperature of the gas is far above the point that is called its
critical temperature.
vessel is varied by the movement of a piston, while simultaneously measuring the pressure p of the enclosed air.
The quantity n of the gas depends on the initial volume V0 into which the
air is admitted through an open valve before starting the experiment.
The law discovered by Boyle and Mariotte states that:
(1)
p ⋅V = const.
E VA L U AT ION
and is a special case of the more general law that applies to all ideal gases.
This general law describes the relationship between the pressure p, the volume V, the temperature T referred to absolute zero, and the quantity n of
the gas:
(2)
As the cross-sectional area A of the piston is constant, the volume V of
the enclosed air can easily be calculated from the distance s travelled by
the piston relative to the zero-volume position. For an exact analysis, the
unavoidable dead volume V1 of the air in the manometer should also be
taken into account.
p ⋅V = n ⋅ R ⋅T
R = 8.314
J
mol ⋅ K
(the universal gas constant).
From the general equation (2), the special case (1) is derived given the condition that the temperature T and the quantity of the gas n do not change.
In the experiment, the validity of Boyle’s Law at room temperature is demonstrated by taking air as an ideal gas. The volume V of air in a cylindrical
OB JEC T I V E
E X P E RIME N T
P R O C EDURE
Measurement at room temperature in air as an ideal gas.
• D
isplaying the measured values for three
different quantities of air in the form of
a p-V diagram.
• Verifying Boyle’s Law.
S UMM A R Y
The experiment verifies Boyle’s Law for ideal gases at room temperature, taking air as an ideal gas in
this experiment. The volume of a cylindrical vessel is varied by the movement of a piston, while simultaneously measuring the pressure of the enclosed air.
1
18.1 mMol
300
200
req uired apparatus
Quantity
9.5 mMol
p / kPa
• M
easuring the pressure p of the enclosed
air at room temperature for different
positions s of the piston.
400
Description
Number
Boyle‘s Law Apparatus
1017366
5.2 mMol
100
0
0
1
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Fig. 1: Pressure/volume diagrams for three different quantities of air at room temperature.
...going one step further
400